Epidemiology and classification of bone tumors.

Primary bone tumors are uncommon and this has certainly contributed to the scarcity of data about their relative frequency, and to the limited understanding of the risk factors. Overall, bone sarcomas account for 0.2% of all malignancies, and the adjusted incidence rate for all bone and joint malignancies is 0.9 per 100,000 persons per year, while the 5-year overall survival rate is 67.9%. The age specific incidence rates of bone sarcomas show a bimodal distribution, with a first peak occurring in the second decade, and a second peak occurring in patients older than sixty, in relation with the age distribution of the main histological subtypes. Several bone tumor types occur in the setting of inherited syndromes, while some other develop in association with non-neoplastic precursors or in the setting of previous benign tumors. In recent years, significant advances have occurred in the molecular and cytogenetic characterization of benign and malignant bone tumors. The detection of clonal chromosomal aberrations, specific molecular genetic changes, and the identification of growth related tumor cell signaling pathways have resulted in a better understanding of the pathogenesis of several neoplastic entities, and have provided the basis for an improvement in the diagnostic workup and differential diagnosis of several bone tumors presenting with overlapping clinical, radiological and pathological features, as well as for the identification of new prognostic factors and therapeutic targets.